The present invention relates to an underwater camera, comprising a pressure-tight housing in which is disposed a camera and a release mechanism which responds as the underwater camera reaches a predetermined distance from the bed of the sea to release the shutter of the camera.
In U.S. Pat. No. 3,261,274 an underwater camera is disclosed which is fixed on a grab for taking samples of the sea bed and is designed to photograph the sea bed from which the sample is taken and before the sampling operation. The release mechanism consists of a heavy ball, which is connected by a relatively long cord to a switch, which is arranged externally of the pressure-tight housing of the camera and is held in the open position by the weight of the depending ball. When the grab is lowered, the ball strikes the sea bed with the spacing which is determined by the length of the cord and, as a result, the cord is relieved of any load and the electric switch is closed and the camera released.
A serious disadvantage of such a release mechanism consists in that the ball coming into contact with the sea bed stirs up the surface of the latter to some amount, depending on the nature of the said bed and, thus, destroys it. Simultaneously, the picture which is taken is blurred. In addition, the instant of release cannot be exactly defined, because, for example, with a soft sea bed such as mud, the ball penetrates for a relatively long distance into the bed before the cord is relieved of weight to such extent that the release operation occurs. Consequently, the distance from which the photographic exposure is made no longer coincides with the range setting of the objective, so that blurred pictures are produced. It is not possible to make allowances beforehand for the penetration of the ball into the sea bed, since the depth of penetration is not known in advance. In addition, time delays are produced by the guiding of the cord, which can also be adversely affected by soiling material, such as sand or mud. These delays are not of a fixed value, so that a further danger of a release taking place at an incorrect distance results.
The constructional design of the release machanism is comparatively complicated and, in addition, the manipulation thereof is difficult. The long cord with the weight, which can easily begin oscillatory movements, can become entanged on board a ship and even lead to faulty exposures. Moreover, the weight can adversely affect the closing of the grab on the sea bed, since it is practically impossibe to hold the weight free from the grab.
A quite important disadvantage of this known release mechanism is in the high weight of the ball used for release purposes. This weight has to be so large that it prevents faulty release actions due to the resistance to flow of the ball in the water as it is sinking and, in addition, that it reliably overcomes the frictional forces in the transmission of the traction by the cord and in the releasing switch. With a free-falling grab, which is provided with a buoyancy element and additional weights, which are discarded on the sea bed, the dead weight is thereby considerably increased, so that correspondingly the useful load is reduced. This also applies to a camera which is not simultaneously connected to a grab, but is used with a freely falling arrangement.
A free-falling arrangement for taking sea bed samples is disclosed in German Auslegeschrift 1,911,782. That arrangement comprises glass balls as buoyancy members, in the uppermost of which is disposed a camera. The releasing of the camera is effected through a cord, which is tightened on one half of the grab and is broken when the grab is closed. As a result thereof a magnet arranged externally of the ball or sphere with the camera in it is moved into the range of magnetically actuated contacts, which are thereby closed and operate the camera shutter electromagnetically.
With this known release mechanism, which became known some years after the arrangement already previously discussed, the disadvantage of the dead weight of a release ball or sphere is avoided, but more serious disadvantages are caused as a result thereof. Releasing of the camera is, in fact, only possible when the grab has come into contact with the sea bottom and commences closing. As the grab approaches the sea bed, however, the surface thereof is stirred up considerably and destroyed by the water flow, which is caused by the descending grab. Moreover, the release always only occurs when the halves of the grab have become operative, as a result of which the surface of the sea bed is also destroyed. Therefore, it is not possible to take unimpaired pictures of the area of the sea bed from which the sample is taken. It is also impossible to avoid this disadvantage by the camera being directed towards an area closely adjacent the grab, as is the case with this known arrangement; for in this case also, stirring effects are also produced at this position by the impacting grab and, in addition, it is not that part of the sea bed from which the sample is taken which is photographed. And, with an obliquely directed camera, it is not possible to produce a sharp definition in all regions of the picture, since the spacing of the exposed parts from the camera is highly variable. Finally, it is also a disadvantage that, when the sea bed is soft and muddy, it is not possible to establish exactly the point of release, since the point of release depends on the amount to which the grab sinks into the mud. It is, thus, impossible to make sharp exposures of the sea bed.
The present invention has for some of its objects to provide a release mechanism for an underwater camera, which is of least possible weight, permits exact release operations, even when the sea bed is soft, is simple to manipulate and, when using a grab especially of the free-fall type, permits accurate exposure of that part of the sea bed from which the sample of the bed is to be taken.
The objects forming the basis of the invention are achieved by the fact that the release mechanism is a measuring means arranged in the pressure-tight housing and operating by ultrasonics, the said means being connected through pressure-tight, electric bushings in the housing with an electro-acoustic transducer arranged externally of the housing and serving for the transmission and the reception of the ultrasonic signals.
The solution according to the present invention avoids any movable parts outside the camera housing. In this way, all the disadvantages which arise with the known arrangements because of parts lying outside the camera housing are avoided. A ball or sphere suspended from a cord or cable for scanning the sea bed is avoided, so that a considerably lower weight is produced and there is no destruction of the sea bed which is to be photographed. The manipulation and construction are also considerably simplified. Since an ultrasonic signal, even with a soft sea bed, responds accurately to the surface of the bed, it is always possible to make accurate and sharp pictures, because the distance for the release can be accurately predetermined. This also leads to the advantage that, when the distance or spacing is accurately known, the size and position of the objects which are photographed can be exactly determined. Because the ball or sphere is not used, the weight is additionally also considerably reduced, so that in those cases where a free-fall arrangement is used, the buoyancy can be lower or the useful load can be larger. This advantage is considerable when the camera involved is an underwater camera which is to be used at great depths, of for example 8000 meters.
The electro-acoustic transducer of the present invention is preferably arranged in an externally disposed recess of the housing, so that it is actually in communication with the surroundings as regards the sound, but lies in a position completely protected mechanically. In an underwater camera for great depths, the formation of a recess in the housing may present strength problems. It is, therefore, desirable for the recess for the electro-acoustic transducer to be arranged in a cover for closing the housing and for this recess to be in the form of a radial bore in a circular cover.
A further feature of the invention includes the range-measuring mechanism which, operating by ultrasonics, generates periodically recurring pulses, which respectively actuate a switch for transmitting the ultrasonic signals and simultaneously triggers a timing member which, when its impressed or imprinted time has expired, actuates a switch which then interrupts the channel for the reflected echo signal from the electro-acoustic transducer to means for operating the release member for the shutter of the camera. By using this procedure, the result is obtained in a simple manner that the echo signal can be directly used for the release, since it is only then that it is able to pass through its transmission channel in the arrangement and cause the release, if it appears before the channel is interrupted.
A further feature of this constructional form consists in that the pulses simultaneously trigger a further timing member, of which the imprinted time is somewhat shorter than that of the first timing member and that, after its impressed time has elapsed, actuates a switch which opens the channel for the reflected echo signal. By this procedure, the transmission channel for the echo is substantially only open for the time within which the echo signal must arrive, when it has scanned the sea bed in the pre-set range. In practice, therefore, a timing window or apertured is formed, through which the echo signal has to pass in order to become effective. Echo signals which, in time, lie before or behind the aperture, cannot become effective. In this way, the danger of faulty exposures is minimized.
For the displacement of the window or aperture as a function of time, it is desirable for the timing members to be adjustable, and it is at the same time desirable that the timing members are adjustable in the same direction by a common actuating means in such a way that the opening time of the channel for the echo signal, as established by the difference of the imprinted times of the two timing members, remains substantially constant with adjustment of the times. It is therefore possible by means of the common actuating means to adjust the response range or distance without any difficulties.
In a further feature of the invention, the reflected echo signal actuates an electromagnet for opening the shutter of the camera and, simultaneously, starts or triggers a timing member which, after expiration of the imprinted time which corresponds to the necessary time for the opening of the camera shutter, actuates an electromagnet for closing the shutter. The opening of the shutter can, thus, be easily effected in this way, and the time of opening naturally being capable of being basically adjustable.
Finally, a further feature of the invention is that the timing member triggered by the echo signal is adjustable together with the timing members for the interruption and opening of the channel for the echo signal, in such a way that, with increasing response range, the imprinted time of the timing member for closing the diaphragm is increased and, thus, the exposure time is lengthened. The result achieved by this feature is that the opening time is dependent on the response range, so that the exposure time is adapted to the picture brightness which is to be expected.
These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.